The use of electrosurgical instruments to perform electrical functions such as cutting and/or coagulation is well known. An example of such an electrosurgical instrument is shown in U.S. Pat. No. 3,699,967, issued Oct. 24, 1972 to Robert K. Anderson and entitled "ELECTROSURGICAL GENERATOR."
In this type of surgery, a radio frequency, (R.F.) current is generated at a generator and then coupled through an output power transformer and capacitors to the active and patient electrodes in the electrosurgical instrument, the electrosurgical function being performed by passing the R.F. current through a patient in contact with the electrodes. As is also well known, surgery is performed at the point where the active electrode is in contact with the patient and to this end the active electrode is normally of small size to achieve high current density at the point of contact with the patient. Since the patient electrode, however, is meant to be surgically inactive, a large area of contact with the patient is desired to thus create a low current density.
While the electrodes of the electrosurgical instrument can have the patient electrode connected with ground to thus provide a grounded output configuration, it has been found advantageous to isolate both electrodes from ground to thus establish an isolated output configuration. The isolated output configuration has been found advantageous in that power can be supplied only between the output terminals, rather than between one terminal and ground. The inability to develop power to ground alleviated a common problem in electrosurgery caused by a break in the patient connection which heretofore has been known to cause power burns at the point of ground contact with the patient. The isolated output configuration also has proved to be advantageous since the patient is not grounded and this reduces the possibility of low frequency ground-completed circuits through the patient which could result in electrocution of the patient.
A disadvantage of the isolated output configuration heretofore, however, has been due to the presence of ground-seeking R.F. leakage currents emanating from either pole of the generator. These leakages are caused by stray capacity to ground on either the active or patient side of the output circuit. Stray capacity on the active side of the output circuit can cause a current to flow between the patient connector and ground if this point is referenced near ground, while stray capacity on the patient side of the output circuit can cause currents to flow between the active side and ground.
Excessive leakage from the active side of the output circuit to ground can bring about a situation where surgery can be accomplished without a patient connection and result in severe risk of R.F. burns to the patient. Excessive leakage from the patient side of the output circuit to ground, on the other hand, can bring about a situation where the patient attains an R.F. voltage with respect to ground and this can result in R.F. burns to the patient and possibly also to operating room personnel having contact with the patient.